1. Technical Field
The present invention relates to the application of braking, through a control lever, on a drilling derrick winch equipped with a band brake located away from the control lever.
2. Background Information
It is known that derricks, used in particular in the oil industry for deep drilling by means of a bit mounted at the end of a drill string, include a winch whose rope actuates the travelling block of a hoist allowing the handling of the drill string during the formation or extension, lowering, raising and dismantling of drill pipes, as well as during drilling operations. In the successive phases of drill string lowering, the winch is braked by means of the band brake with which it is equipped and which is actuated by an operator using a control lever. Since the structure of a derrick and the drilling elements such as the winch, rope and lifting hoist, mud injection swivel, kelly, drill pipes, drill collars and drill bits are well known to those of the art, we shall not dwell upon these points in the description of the invention.
According to a conventional arrangement, the control lever acts mechanically directly on the band of the brake. To enable the operator to observe the operations performed on the drill string, the winch should be placed near the rotary table which imparts rotation to the drill string through the kelly. This arrangement has the drawback of taking up room on the working platform around the rotary table, capable of hindering operations on the drill string. Moreover, the winch constitutes a considerable load for the platform.
To overcome these drawbacks, one prior art approach is to move the winch away from the rotary table and place it, for example, on the ground or on a lower platform of the derrick support structure, thus freeing and lightening the weight on the working platform. The control lever, remaining on the platform, is then linked with the band brake of the winch by either mechanical (control linkage) or hydraulic transmission means. Satisfactory actuation of the band brake is however not achieved owing to the play and lack of rigidity inevitable in a mechanical transmission system, or slow response times of the elements of a hydraulic transmission system. And, the braking of a derrick winch, owing to self-blocking phenomena, must be extremely precise and calls for considerable sensitivity and skill on the part of the operator, to avoid catastrophic consequences for the drill string, being poorly suited to such transmission imperfections between the control lever and the band brake. In the case of hydraulic transmission, problems are also encountered during the installation and removal of hydraulic transmission lines (due in particular to the complexity of the operations and to the risk of losing hydraulic fluid or polluting this fluid).